I used to be a Cinemar/MainLobby user, so I'll try to answer from (distant) memory:
MainLobby started out primarily as a PC-based home control application and has subsequently branched out to include iOS and Android 'client' modules - so to answer your question: you need a Windows-based PC to "host" the application (acting as a server), and then another device, be it a PC or smartphone/PDA, to act as the client (the client & server code can reside on the same PC).
As I presume you will have seen, the application is very 'modular' - some modules are free and others are for fee. To play music you need MainLobby and MLServer modules, PLUS the MusicLobby module. I haven't looked recently, but I suspect that you may need to spend $3-400 just to control & play music. For that money you get some great pre-designed screens and icons, as well as a very 'tried and tested' application. As an aside, Mario and David provide great support and are both really stand-up guys.
Importing music into MusicLobby is really easy and there is a very capable "auto-tag" function that can bring in lots of additional information for each track.
In one of your later posts you mentioned controlling videos (trailers, now_playing, etc.) - to do this requires the addition of yet another module - DVDLobby. At a cost of another >$100 (I'm guessing)
You haven't provided a lot of details about your setup, but to control devices like TVs, amplifiers, etc. will obviously require some form of connectivity, such as IP, IR, or serial - the latter two will definitely require additional hardware (like a Global Cache iTach, etc.).
I spent many hundreds of dollars on Cinemar products and at the time there was nothing much else around that had the flexibility or capabilities of the MainLobby suite, at the price point I was comfortable with. The landscape has changed significantly over the last few years, so you need to decide exactly what functionality you're looking for (and how much you want to spend). Suites like MainLobby and CQC/Charmed Quark reside towards one end of the spectrum, and apps like Roomie, iRule, etc. are at the other - every one of these has it's own pros and cons, each has a its' own set of characteristics and unique value proposition.
Sorry if some of this is stating the obvious, but hopefully some of it helps a bit!